Role of proximal CACCC box in initiation of GATA-1 expression and existence of a negative control element. GFP expression patterns in 9 to 12 somite embryos microinjected with three critical GATA-1/GFP linearized constructs: (A) G1-GM2 produces strong GFP expression; (B) G1m-GM2 produces weak GFP expression; and (C) DE139 shows no GFP expression at all. Zebrafish embryos at the 18- to 19-hour stages transgenic for G1-GM2 (D) or DE1776 (E) show similar patterns of GFP expression. GFP is expressed in the notochord (indicated by an arrow in F) of embryos transgenic for DE468, although GFP is also present in abundance in the hematopoietic intermediate cell mass. Similar results were observed in germline fish transgenic for DE421 (data not shown).